[A Case of Biopsy Confirmed Unresectable Retroperitoneal Seminoma Successfully Treated with Chemotherapy].

We herein report a case of a retroperitoneal tumor of unknown origin that was diagnosed as a seminoma after tumor biopsy and was successfully treated with chemotherapy containing bleomycin, etoposide, and cisplatin(BEP). A 47-year old man visited our hospital with left abdominal pain. An endoscopic examination revealed an ulcer lesion on the third part of the duodenum. Abdominal CT scan revealed a retroperitoneal tumor invading the abdominal aorta with the tumor thrombus in the inferior vena cava(IVC). An endoscopic biopsy could not identify the tumor's origin because of the negative staining of various surface markers on immunohistochemistry. Surgical biopsy of the unresectable retroperitoneal tumor that was finally diagnosed as a seminoma was performed. The patient was treated with BEP according to the International Germ Cell Consensus Classification(IGCCC)for risks, and orchiectomy was performed. He has been alive for 7 months with progressive shrinkage of the retroperitoneal tumor, in which 18F-fluorodeoxyglucose(FDG)positron emission tomography(PET)has shown a dramatic reduction of the maximum standardized uptake value(SUV)during chemotherapy.